With increasing interest in employing light for information transfer theoretically useful models of spatial light modulators (commonly referred to as SLM's) have been proposed.
It has been observed that light being transmitted through a medium can be modulated by spatially intersecting light from a second source when the medium exhibits a refractive index that can be varied in response to light transmission. By "spatially intersecting" it is meant that light from the separate sources traverses intersecting paths, but not necessarily within overlapping time periods. The effect, referred to as a photorefractive effect, was first observed in working with lithium niobate (LN), lithium tantalum niobate (LTN), and potassium tantalum niobate (KTN) crystals intended for second harmonic generation (SHG) applications. Observations of photorefractive effects allowing holographic images to be stored in LN and KTN are reported in Chapter 11, Optical Phase Conjugation in Photorefractive Materials, Optical Phase Conjugation, Academic Press, 1983, pp. 417-425.
G. Model, K. M. Johnson, W. Li, and R. A. Rice, "High Speed Binary Optically Addressed Spatial Light Modulator", Appl. Phys. Lett., Vol. 55, No. 6, Aug. 7, 1989, pp. 537-539, illustrated a photorefractive light modulating device which employs liquid crystals as a photorefractive material. Although Moddel suggests that the ferromagnetic liquid crystals employed represent an improvement in terms of switching speeds over nematic liquid crystals, the fact is that all liquid crystal photorefractive devices are inherently limited in their frequency response, since the entire liquid crystal molecule must change its orientation to effect switching.
Another significant disadvantage of liquid crystals employed to provide photorefractive effects is that separate aligning layers must be provided above and below the liquid crystal layer to achieve the best attainable response. This involves constructing three separate layers and is consequently a fabrication disadvantage. The use of a liquid crystal layer between alignment layers is illustrated by E. M. Yeatman and M. E. Caldwell, "Spatial Light Modulation Using Surface Plasmon Resonance", Appl. Phys. Lett., Vol. 55, No. 7, Aug. 14, 1989, pp. 613-615.
R. Lytel, F. G. Lipscomb, J. Thackara, J. Altman, P. Elizondo, M. Stiller and B. Sullivan, "Nonlinear and Electro-Optic Organic Devices", pp. 415-426, Nonlinear Optical and Electroactive Polymers (P. N. Prasad and D. R. Ulrich, editors), Plenum Press, N.Y., 1988, disclose in FIG. 1 at page 419 a spatial light modulator comprised of a photodiode for receiving modulating light, a light blocking layer, a dielectric mirror, an electro-optic crystal and a transparent electrode for external circuit connection to the photodiode. While it is speculated that organic electro-optic materials might be substituted for the electro-optic crystal, the device even when so modified remains quite complicated to construct and limited in potential configurations because of the photodiode addressing required.
D. J. Williams, "Organic Polymeric and Non-polymeric Materials with Large Optical Nonlinearities", Angew. Chem. Int. Ed. Engl. 23, (1984) 690-703, illustrates the known relationships between polarization properties and organic molecular dipoles.